This is a continuation of International Application No. PCT/EP98/07893, with an international filing date of Dec. 4, 1998, which is based on German Patent Application No. 197 54 000.7, filed Dec. 5, 1997.
The invention relates to a dispensing head set up for the time-controlled, electrically triggered release of microdrops, in particular, to a multi-channel dispensing head with separately triggerable micropipettes, and a procedure for using such a dispensing head.
Dispensing heads or modules are widely used for tasks in biotechnology or chemical technology for the controlled release of small volumes of liquid in the form of microdrops. One example of this is the fabrication of miniaturized DNA arrays for genetic engineering applications, wherein a small drop size yields a high cloning density, for which piezoelectrically activated micropipettes are particularly well suited. DNA clones, microorganisms, cells, cell constituents or biomolecules are normally stored as active substances in microtiter plates with numerous recesses (e.g., 96 or 384). Rapidly fabricating arrays consisting often thousand different DNA sequences, for example, requires dispensing modules that can convey liquids from microtiter plates to substrate surfaces for combination purposes in a highly parallel manner or at a sufficient serial rate.
It is generally known that single-channel dispensing heads or multi-channel dispensing heads can be used in the form of a linear sequential arrangement of micropipettes. These conventional dispensing systems exhibit the following disadvantages.
When using a single-channel dispensing head with a single micropipette, the substances to be combined must be conveyed from a reservoir (e.g., microtiter plate) to a reaction substrate, wherein a cleaning step is required during each substance change. This procedure is unacceptable for practical applications in combinatory biotechnology or chemistry because it is time-intensive.
While multi-channel dispensing heads, which essentially consist of a series of 8 to 16 single-channel dispensing heads, do make it possible to reduce the time outlay due to the parallel operation of individual micropipettes, the mounting and control equipment they require is still expensive. Since every individual micropipette is equipped with two control lines for activating the piezo element, and a liquid line for applying a rinsing or charging pressure, conventional multi-channel dispensing heads are complex and cumbersome arrangements.
For example, in the case of a dispensing head with a series of 8 electrically activated micropipettes, a total of 16 control lines and 8 pressure lines would have to be incorporated, all connected with corresponding individual control and pressure devices. If such a multi-channel dispensing head is to be passed over a substrate with an x-y-z positioning device, the complex design of the dispensing head constitutes a crucial disadvantage for the accuracy of dispensing head positioning due to the weight and required inclusion of numerous individual lines. However, imprecise microdrop placement limits the effectiveness of conventional dispensing systems in an unacceptable manner.
Another disadvantage lies in the relatively high susceptibility of the sequentially arranged single-channel micropipettes to failure. Finally, each of the sequentially attached single-channel dispensing heads requires so much space that the micropipette tips have greater distances than the conventional modular dimensions of microtiter plates. This makes a substance absorption by microtiter plates ineffective.
Thus, it would be advantageous to provide an improved multi-channel dispensing head distinguished, in particular, by a simplified design, simplified controllability, reduced reaction time and elevated positioning accuracy. It would also be advantageous to provide improved applications for such a dispensing head.
The basic idea of the invention is to provide a multi-channel dispensing head in which micropipettes are arranged on a shared carrier in a two-dimensional or planar manner each with an electrically actuatable trigger device, which has a ground and signal terminal, the carrier having a ground or signal contact for each ground and signal terminal, wherein the ground and signal contacts on the carrier are arranged in two planes separated and electrically insulated from each other. The contacts on the carrier are spaced apart relative to the axial expansion (or longitudinal expansion) of the micropipettes. This configuration enables a greatly simplified design with a more compact micropipette arrangement.
The invention can be realized with many kinds of micropipettes that are equipped with an electrically actuatable trigger device and set up to release a microdrop after a pressure pulse is triggered in the volume of the micropipette. The trigger device can be a piezo device, a valve arrangement (in combination with a pressure line) or any corresponding electrical pressure device. The two-dimensional or planar arrangement of micropipettes on a shared carrier can encompass any regular or irregular arrangement. However, a regular arrangement with straight or concentric rows is preferred.
In a rectangular matrix arrangement, the micropipettes form rows and columns aligned at a right angle to each other. In an oblique-angled matrix arrangement, the micropipettes form straight rows and columns that are aligned obliquely (not perpendicular) to each other. In a circular arrangement, the micropipettes form concentric circles. In the latter case, the rows and columns mentioned below are formed by radially arranged (straight) micropipette rows and circular micropipette rows.
In a first embodiment, the dispensing head according to the invention includes one or more micropipette rows on a shared carrier, wherein the ground contacts of each series are electrically interconnected, and the signal contacts are separately actuatable with a signal demultiplexer circuit.
In a second embodiment, the dispensing head according to the invention includes one or more micropipette rows on a shared carrier, wherein the signal contacts of all rows are electrically interconnected, and the ground contacts are separately actuatable with a demultiplexer circuit.
In a third embodiment, the dispensing head according to the invention includes numerous micropipette series in which the micropipettes are two-dimensionally allocated in columns and rows in the form of a matrix. In this embodiment, the ground contacts of each series are electrically connected, wherein,a ground demultiplexer circuit is provided, with which the shared ground contacts of the individual micropipette rows are separately actuatable. In addition, the signal contacts of each micropipette column are electrically interconnected, wherein the signal demultiplexer circuit is provided to make the combined signal contracts of the micropipette columns separately actuatable.
The demultiplexing technology makes it possible to actuate precisely one trigger device of a micropipette whose position corresponds to the selected row or column by applying the ground or signal potential to one of the rows or columns.
The subject of the invention is also a micropipette with an electrically actuatable trigger device, which has a ground and signal terminal, and exhibits two attachment devices. Each of the attachment devices performs a dual function. First, an attachment device is provided on a carrier or mount to establish an electrical connection between the ground or signal terminal and corresponding electrical control terminals. Second, the attachment devices themselves act as a mechanical coupler or attachment means to secure the micropipette to the carrier or mount. The attachment devices provide a mechanically secure link between the micropipette and carrier or mount, and encompass soldering tags, spring elements or threaded necks.
In an advantageous configuration of the micropipettes, a pressure line connects each micropipette with a distributing device also secured to the carrier, through which charging or cleaning pressure can be imparted to the micropipettes. The distributing device may be either a multi-valve arrangement or a valve-free branch piece.
The micropipettes exhibit a loading volume to receive the working substance to be released in microdrops, and a carrier volume to receive a carrier liquid. In a preferred procedure of the invention, the dispensing head is charged in such a way that a carrier liquid is first received simultaneously in all carrier volumes of the micropipettes. Specific working substances are then received by each micropipette at a working substance reservoir arrangement comprised of numerous reservoirs, which are each aligned in accordance with the micropipette arrangement at the dispensing head. The trigger device is situated in the area of the carrier volume, so that the microdrop release takes place by actuating the trigger devices and imparting the pressure pulse via the carrier liquid to the respective working substance.